Both the cost of maintaining a drilling rig for such purposes as drilling oil wells and the complexity of underground formations encountered in deephole drilling, have led to the need for the ability to drill multiple, angled or deflected drill holes from a single drilling platform.
This process of directional drilling has involved improvements and innovations both in the construction of the actual drilling subs and drill bits for use at the bottom end or drilling end of a drill string as well as significant improvements in the instrumentation necessary to control and monitor the downhole progress of the drilling.
For the purposes of this patent application, it is necessary only to point out that within the arts technique known as wireline tools have been devised. These tools, which are lowered through the inner tubular region of a drill string to a point adjacent the actual drilling bit permit monitors on the surface or floor of the drill rig to determine the angle, depth, and general environmental conditions being encountered by the drill bit. In particular, it is possible, using current wireline technology to establish orientation within a downhole drilling sub and to determine positively the existing downhole rotational orientation and angle of drilling orientation at any point within the drilling process.
Drilling subs or directional drilling currently known to the art are two major constructions. In the first, designed principally for use when the rotation energy imparted to a drill that is imparted by rotating the entire drill string from rotation imparted by a rotating table installed on a drill rig floor, or angled subs; that is, the drilling sub is constructed at a permanent offset so that rotation entered at the top of the sub is angled and proceeds to rotate the drill bit at an offset angle at the bottom of the sub. These units are in essence very large analogs to an angled drive collet known in the drill art and machine shops and the like. In order to engage in drilling using such a sub, the entire drill string must be tripped out, the appropriate angled sub installed, the drill string re-entered into the bore and drilling using the angled sub commenced. The total amount of deflection is the function of the distance drilled while the angled sub is installed. When the desired deflection has been achieved, the entire drill string must again be tripped out, the angled sub removed, and straight subs re-installed so as to permit continued straight line drilling at the new, deflected direction.
In the field of downhole drill motors, such as the turbine drilling devices, driven by mudflow and the like, it is possible to create an angled deflection by controlling the flow of the mud preferentially out one portion of the drill bit. Such apparatus are known, and are widely used.
The primary cost and difficulty encountered in current art directional drilling devices is the general necessity that for each change of direction at least two trips of the drill string are required to install and remove the directional drilling apparatus. Such drill string activity is nonproductive, considerably slows the drilling process, and introduces other problems such as drill string sticking, possible hole collapse and the like, all of which are well known to the art. It is therefore considered higly desirable that the number of trips of the drill string during the drilling operation be minimized, and that the amount of time actually spent drilling be maximized. This is especially true on an offshore platform where all the wells drilled are usually drilled from an initial starting bore and where the success of the offshore drilling platform is totally dependent upon the ability to engage a multiple directional drilling.